Objectives: This is a study and accessioning of cancer in laboratory animals, involving collection and development of competence in special areas of cancer morphology. We will study histopathological and fine structure alterations related to the pathogenesis of disease induced by oncogenic viruses and other carcinogens. Major findings: An ongoing program has been the development of special competence in the histopathological and fine structural aspects of tumors of the lung, bone and mammary glands of rodents. Collection and examination of induced and naturally occurring bone tumors has been in progress for more than 5 years and will continue. The collection and development of competence in lung tumors is essential for the work previously described, and additionally serves as an aid to other investigators in the area and to the NCI Registry of Experimental Cancers. A current project on which Ms. May serves is the study of the fine structure of the early squamous metaplasia preceding carcinoma at the site of implanted carcinogen pellets, and the comparison of this change with the metaplasia associated with non-specific pulmonary inflammation which does not progress to cancer. Interest in mammary neoplasia in rats is an offshoot of current long-term pulmonary experiments. Since over 50% of female strain OM rats develop mammary tumors in the second year of life, it is necessary to surgically remove these in our experimental groups. As a result we have correlated data on incidence, growth rate and morphology in several hundred excised mammary neoplasms. Proposed course: We have, through the past 5-6 years, acquired an extensive catalog of neoplasms of all types that develop in aged female Osborne-Mendel rats. This data will be collated in an effort to establish normal incidence rates for our colony.